1. Field of the Invention
The present invention relates to a refrigerant compressor, and more particularly, to a slant plate type compressor with a variable displacement mechanism, such as a wobble plate type compressor with a variable displacement mechanism for use in an automotive air conditioning system.
2. Description of the Prior Art
FIG. 1 illustrates a wobble plate type compressor with a variable displacement mechanism as disclosed in U.S. Pat. No. 4,606,705 to Parekh et al. For purposes of explanation only, the left side of the figure will be referenced as the forward end or front and the right side of the figure will be referenced as the rearward end.
Compressor 100 includes compressor housing 101, cylinder block 102 having a plurality of cylinders 103 formed therein, driving mechanism 104 having drive shaft 105 and slant plate 106, wobble plate 107 which is rotatably mounted on slant plate 106 and nutates when drive shaft 105 and slant plate 106 rotate, and rotation preventing mechanism 108 which prevents rotation of wobble plate 107 during the nutational motion of wobble plate 107. Pistons 109 are slidably disposed in respective cylinders 103 and are connected to wobble plate 107 through respective connecting rods 110. The nutational motion of wobble plate 107 causes pistons 109 to reciprocate in respective cylinders 103 and thereby compress the refrigerant therein. Crank chamber 111 is defined by housing 101 and a front end of cylinder block 102. Suction chamber 112 is defined in housing 101 rear to cylinder block 102. Valve control mechanism 113 is disposed in housing 101 and controls the communication between crank chamber 111 and suction chamber 112 in response to changes in suction chamber pressure in order to vary crank chamber pressure. Changes in the crank chamber pressure varies the slant angle of slant plate 106 with respect to a plate perpendicular to the axis of drive shaft 105. In turn, changes in the slant angle of slant plate 106 varies the stroke length of each piston 109 so that the capacity of compressor 100 changes. Therefore, the capacity of compressor 100 is varied by the operation of valve control mechanism 113.
An inner front end of drive shaft 105 is rotatably supported by a front end of housing 101 through needle bearing 101a. Thrust needle bearing 101b surrounding drive shaft 105 is disposed between an inner end surface of the front end of housing 101 and a front end of annular cylindrical member 114 fixedly connected to drive shaft 105 by pin member 115. Thrust needle bearing 101b receives a forward force generated by the gas pressure reaction force of the compressed refrigerant in cylinders 103 as transmitted through pistons 109, connecting rods 110, wobble plate 107, slant plate 106, drive shaft 105 and annular cylindrical member 114.
First annular groove 105c is formed in an outer peripheral surface of the inner rear end portion of drive shaft 105 in front of forward to cylinder block 102. Split ring return spring 116 is fixedly received in first annular groove 105c by snap portion 116a. When slant plate 106 reaches its minimum slant angle, it is contacted by return spring 116, and the restoring force of split ring return spring 116 urges it back towards greater slant angles. Therefore, when slant plate 106 contacts split ring return spring 116, a rearward force acting on drive shaft 105 is generated. The rearward force is increased in direct proportion to the increase in the restoring force of return spring 116. When the rearward force generated by the contact of slant plate 106 and return spring 116 becomes greater than the forward force generated by the gas pressure reaction force in cylinders 103, drive shaft 105 tends to move rearwardly.
Referring also to FIG. 2, drive shaft 105 includes small diameter portion 105a which is integral with and extends from an inner rear end of drive shaft 105, thereby forming annular ridge 105b at the inner rear end of drive shaft 105. Annular ridge 105b is located in front of cylinder block 102. Small diameter portion 105a of drive shaft 105 is rotatably supported by cylinder block 102 through needle bearing 102a which is fixedly disposed in central bore 117 formed through cylinder block 102. Needle bearing 102a is fixedly disposed in central bore 117 by, for example, forcible insertion.
Second annular groove 105d rearwardly extending from annular ridge 105b is formed in an outer peripheral surface of small diameter portion 105a of drive shaft 105. Washer 118 is slidably received in second annular groove 105d, and is sandwiched between annular ridge 105b and cylinder block 102 so as to prevent the rearward movement of drive shaft 105. The axial length of second annular groove 105d is designed to accommodate a washer 118 having a sufficiently large thickness. Washer 118 radially extends in order to contact the front end surface of cylinder block 102.
When this prior art compressor is assembled, the clearance created between a side wall of annular ridge 105b of drive shaft 105 and the front end surface of cylinder block 102 is variable because of a variation in the tolerances of the compressor component parts. Therefore, the washer 118 that is selected has a thickness equal to or slightly smaller than the clearance created between the side wall of annular ridge 105b and the front end surface of cylinder block 102 in order to effectively prevent the rearward movement of drive shaft 105.
However, as drive shaft 105 tends to move rearwardly, drive shaft 105 thrusts annular ridge 105b rearwardly through washer 118, which is selected to have a thickness equal to or slightly smaller than the clearance created between the side wall of annular ridge 105b and the front end surface of cylinder block 102. Therefore, washer 118 is compressedly sandwiched by cylinder block 102 and annular ridge 105b when drive shaft 105 tends to move rearwardly. As a result, washer 118 rotates relative to cylinder block 102 or drive shaft 105 and frictionally slides over the front end surface of cylinder block 102 or the side wall of annular ridge 105b. In a short period of time, the operation of the compressor causes an abnormal abrasion on the friction surface of the softer member of drive shaft 105 or washer 118, and the softer member of washer 118 or cylinder block 102.
Accordingly, even though the thickness of washer 118 is appropriately selected during the assembling process of the compressor, a new clearance is created between the side wall of annular ridge 105b of drive shaft 105 and the front end surface of cylinder block 102 such that washer 118 may collide with the front end surface of cylinder block 102 and the side wall of annular ridge 105b of drive shaft 105. The collision between washer 118 and cylinder block 102 and annular ridge 105b causes an offensive noise.
Furthermore, if washer 118 is mistakenly selected such that the thickness thereof is smaller than the clearance created between the side wall of annular ridge 105b and the front end surface of cylinder block 102, washer 118 may also collide with the front end surface of cylinder block 102 and the side wall of annular ridge 105b of drive shaft 105 because washer 118 is slidably received in second annular groove 105d. In this instance, the collision between washer 118 and cylinder block 102 and annular ridge 105b also causes an offensive noise.
Still further, selecting a washer 118 that has a thickness equal to or slightly smaller than the clearance created between the side wall of annular ridge 105b and the front end surface of cylinder block 102 complicates the assembling process of the compressor.
FIG. 3 substantially illustrates the relevant part of a wobble plate type compressor with a variable displacement mechanism as sold in the commercial market. In the drawing, the same numerals are used to denote the corresponding elements shown in FIGS. 1 and 2 so that an explanation thereof is omitted.
In this prior art embodiment, thrust bearing 120 is slidably mounted about small diameter portion 105a of drive shaft 105 between the side wall of annular ridge 105b and the front end surface of cylinder block 102. Thrust bearing 120 radially extends so as to contact the front end surface of cylinder block 102. Thrust bearing 120 is selected such that the thickness thereof is equal to or slightly smaller than the clearance created between the side wall of annular ridge 105b of drive shaft 105 and the front end surface of cylinder block 102. Thrust bearing 120 effectively receives the rearward thrust force generated when drive shaft 105 tends to move rearwardly so that no abnormal abrasion occurs on the front end surface of cylinder block 102 or the side wall of annular ridge 105b.
However, the provision of a relatively expensive thrust bearing 120 causes an increase in the manufacturing cost of the compressor.
Furthermore, if thrust bearing 120 is mistakenly selected such that the thickness thereof is smaller than the clearance created between the side wall of annular ridge 105b and the front end surface of cylinder block 102, the associated drawbacks, such as the collision between thrust bearing 120 and cylinder block 102 and annular ridge 105b, will also occur as discussed above for Parekh et al.
Still further, selecting a thrust bearing 120 such that the thickness thereof is equal to or slightly smaller than the clearance created between the side wall of annular ridge 105b and the front end surface of cylinder block 102 complicates the assembling process of the compressor, as it also did in Parekh et al.
FIG. 4 substantially illustrates the relevant part of a wobble plate type compressor with a variable displacement mechanism as disclosed in Japanese Patent Application Publication No. 1-267374. In the drawing, the same numerals are used to denote the corresponding elements shown in FIGS. 1 and 2 so that an explanation thereof is omitted.
In this prior art embodiment, thrust bearing 120 and belleville spring 121 disposed rearward to thrust bearing 120 are mounted about small diameter portion 105a of drive shaft 105 between the side wall of annular ridge 105b and the front end surface of cylinder block 102. Thrust bearing 120 is slidably mounted about small diameter portion 105a. Spring 121 is compressedly sandwiched between thrust bearing 120 and cylinder block 102 such that thrust bearing 120 is continuously urged forward by virtue of the restoring force of spring 121. Therefore, even though the clearance created between the side wall of annular groove 105b and the front end surface of cylinder block 102 is varied, the clearance is accommodated by spring 121 acting through thrust bearing 120, without selecting the thickness of thrust bearing 120. Furthermore, thrust bearing 120 effectively receives the rearward thrust force generated when drive shaft 105 tends to move rearwardly so that no abnormal abrasion occurs on the front end surface of cylinder block 102 or the side wall of annular ridge 105b.
However, since thrust bearing 120 is continuously urged forward by the restoring force of belleville spring 121, the rolling friction between the component parts of thrust bearing 120 is increased, and consequently, the life of thrust bearing 120 is decreased. Furthermore, the provision of a relatively expensive thrust bearing 120 causes an increase in the manufacturing cost of the compressor. And still further, the provision of belleville spring 121 in addition to thrust bearing 120 causes an increase in the number of component parts of the compressor.
In another prior art compressor, Japanese Patent Application No. 60-259776A discloses a variable displacement compressor in which a bearing is disposed within the cylinder block. The cylinder block comprises a bore having a large diameter portion and a small diameter portion with a shoulder therebetween. The bearing is disposed in the large diameter portion such that a portion of the outer race extends radially beyond the shoulder while another portion of the outer race does not extend beyond the shoulder.
During assembly of the '776 compressor, if a rearwardly directed force is applied to the bearing through the small diameter portion of the bore so that the bearing snugly engages the end of the drive shaft, an uneven distribution of force is likely applied to the outer race. This is due to the bore configuration whereby only a portion of the outer race extends beyond the shoulder. Consequently, these nonuniform forces could damage the bearing and lead to its premature failure.